This application discloses an invention which is related, generally and in various embodiments, to a dual-mode encoder, a system including the same, and a method for generating infra-red (IR) signals. Some of the generated IR signals are decodable by an analog headphone and other of the generated IR signals are decodable by a digital headphone.
At one time in the automotive industry, a vehicle came equipped with a single source of audio (e.g., a radio). When the audio source was turned on, the audio from the audio source was presented throughout the entire vehicle via one or more speakers connected to the audio source. Today, many vehicles come equipped with multiple sources of audio. Such audio sources may include a tuner, a CD player, a DVD player, a video game console, a satellite radio receiver, etc. When all of the vehicle occupants are listening to audio from a single audio source, the audio may be enjoyed throughout the vehicle without interference. However, when one of the vehicle occupants is listening to audio from one audio source and another of the vehicle occupants is listening to audio from another audio source, the two audios may overlap, thereby reducing the listening pleasure of all of the occupants.
To address this problem and meet the desires of many vehicle owners, more and more vehicles are now being equipped with the ability to transmit wireless signals, which are associated with one or more of the audio sources, to one or more headphones which are utilized by one or more of the vehicle occupants to enjoy audio from the different audio sources. This allows for audio from one audio source to be presented through the vehicle's speakers, and audio from another of audio sources to be presented through the headphones, thereby minimizing the potential overlap of the two audios.
There are essentially two different categories of headphones, those capable of receiving industry standard analog FM modulated audio signals, hereafter referred to as “analog headphones”, and those capable of receiving digital signals, hereafter referred to as “digital headphones”. For a typical automotive entertainment system which utilizes analog headphones, the audio signals generated by the audio source are input to a circuit which FM modulates certain known carrier frequencies and drives IR light emitting diodes (LEDs). While this operation is typically accomplished entirely with analog circuits it is also possible with mixed signal circuits. For example the audio signals input generated by the audio source are input to operational amplifier circuits for signal conditioning, the outputs of the operational amplifier circuits are input to analog-to-digital converter circuits, and the outputs of the analog-to-digital converter circuits are input to a digital encoder. The encoder employs frequency modulation to modulate the digital signals onto selected carrier frequencies. The output(s) of the encoder (i.e., the modulated signal) is then input to an IR emitter circuit(s). The IR emitter circuit converts the modulated signal into IR light, and the IR light (i.e., the wireless signal) is detected by the analog headphones. The analog headphones include a receiver which amplifies the wireless signal, demodulates it, and filters it to a frequency range suitable for the headphone user.
Although the above-described system mitigates the problem of overlapping audio, the performance of the system is often found to be less than desirable. For example, the fidelity of the audio presented to the headphone user is often worse than that of the vehicle's FM radio, and considerable background static and hiss become more noticeable as the volume of the presented audio is increased.
In general, automotive entertainment systems which utilize digital headphones offer superior performance. Some of the “digital” automotive entertainment systems typically allow for the concurrent transmission of wireless signals associated with a plurality of audio sources, and some of the digital headphones allow the headphone user to select which of the audio sources he or she wishes to listen to. However, because the analog automotive entertainment systems and the analog headphones currently have a lower initial cost than the digital counterparts, more vehicles still come equipped with the analog automotive entertainment systems and analog headphones than the digital counterparts despite the superior performance offered by the digital counterparts.